Latching Circuit for hour meter

[TimK]

I have a commercial machine that has the following voltages available. 480 3 phase (main) 220V AC and 24V DC. I need to connect a 24V DC hour meter that runs only when the main motor is running. Normally I would connect the hour meter to the control voltage pulling down the contactor for the main motor. However this machine uses a motor drive (inverter) to control the main motor.

I am looking for a way to us a N.O. momentary switch (added to the current start Button) to latch a circuit that uses the available 24V DC to power a 24V DC hour meter. And then a N.C. momentary switch (added to the current stop Button) to stop the hour meter.

an example circuit would be great. Is there an electronic way to do this. Most examples of a latching relay us a relay with a 12V coil.

Thanks

 

[OlPhart]

Why not tap the 480 AC with a 120V->6V transformer & rectify the output to run the 24VDC? Or tap the 220 AC with a 120V->12V; same result... <<<)))

If the motor drive/inverter isn't a stable source, what's the inverter input power: tap it.

 

[Reloadron]

We just installed a few VS (Variable Speed) inverters for some pump motors. The drives use a 24 VDC digital input for their RUN command. I just hung a few hour meters across the RUN lines. Next, does the motor control panel have a lamp that indicates the drive is running? There might be something there you can use. What commands the inverter to run?

If the start / stop buttons are standard 22mm or 30mm operator type that use contact blocks, then you could get a NO and NC block and add them as you suggest and add a DPDT 24 VDC coil relay. Then run the hour meter off that as you mention but I would be looking for something simpler first.

Ron

 

[TimK]

The control voltage for the drive is 220V ac

 

[Reloadron]

The control voltage for the drive is 220V ac

That sort of sucks. I would start thinking real serious about your ideas of adding a few contact blocks to existing switches. That or use a small 220 vac relay to switch 24 vdc to your hour meter. Unless you want to find a 220 vac hour meter.

Ron

 

[TimK]

would it be possible to use a couple of transistors and the two switches to make a latching circuit powered by the available 24V DC to power the hour meter. I am sure the current draw would be very small.

Thanks

 

[Reloadron]

You don't need the transistors. Just a simple relay latching circuit. Let me see if I have an example.

Ron

 

[Reloadron]

Attached is a basic relay latching circuit. You would add a switch block to your start/stop push button switches. The pin numbers on the relay contacts are based on an 11 pin Omron MK3 series 24 volt coil relay. If you have existing DIN rail available I would use it to mount the latching relay. The diode across the relay is a snubber. The lamp is just a TM1 ON indicator. It should work. The relay coil is obviously 24 VDC.

Ron

 

[TimK]

This is perfect, I think I can convert this to use the Omron G2R-2-SND which we use a lot of already for other machines. it has the diode and the led built in.

 

[KeepItSimpleStupid]

Another idea, although not necessarily simpler is to use a current sensing relay like from SSAC Timers & Controls Home Page and use this on one of the three phases to enable the timer.

Make sure that internally there isn't a signal available by talking to the mfr.